This invention relates to filament-wound pressure vessels and, more particularly, to pressure vessels having geodesic domes with polar openings and which are filament-wound with a continuous filament that is subject to isotensoid loading upon pressurization of the vessel.
Filament-wound pressure vessels have been widely accepted as vessels for the containment of pressurized fluid in those applications that require high stress levels and low density, excellent corrosion, impact, shatter resistance, and highly predictable burst and cycle characteristics. Various winding patterns have been employed for pressure vessels, and those patterns are typically circumferential or hoop winding, helical winding, and polar winding. The winding patterns of a domed pressure vessel must be carefully chosen to prevent fiber slippage and shear loads on the filament. An ideal dome shape for pressure vessels is an isotensoid or geodesic dome, or end closure. The shape of this dome depends upon the diameter of the pressure vessel and the diameter of the polar opening in the vessel. According to the prior art, such a geodesic dome surface is a surface of revolution requiring a numerical solution for each polar opening diameter and pressure vessel diameter. This solution enables one to progressively plot the curvature of the dome from the diameter of the pressure vessel toward the polar opening. This mathematical progression, however, becomes indeterminent at an inflection point at a radial location of 1.22r.sub.0 where r.sub.0 is the radius of the polar opening. In standard prior art design procedures, a fitting or boss having an outer radius which is greater than 1.22r.sub.0 is inserted in the tank, and the winding surface over the boss is commonly conical or spherical. Since the boss, in effect, eliminates the inflection point, shear stress on the filament is avoided. The provision of such a boss greatly increases the cost of the pressure vessel and its weight.